Re: Convention contracts
"This is often called "outboarding," and is frowned on by basically the entire trade show industry."
Be that as it may, but "frowned upon"is not a legal basis for action. Surely since IGEL is a VMWare partner who had exhibited at VMWorld in previous years, and VMWare staff were among those attending IGEL's event, then VMWare should have known that IGEL wasn't exhibiting at their show AND that they were holding their own show next door. In that case the approach to take would have been to have a polite chat with IGEM, or else ask MGM's restaurants / other venues to refuse IGEM's booking request.
But IGEL had contracts in place with the restaurant that were unilaterally broken by the restaurant, meaning the restaurant is itself liable. If the restaurant did this at the behest of MGM with the threat of not having their lease renewed, that is blackmail and MGM is liable for that. If VMWare pressured MGM (again maybe under threat of not hosting their event there again), that's also basically blackmail for which VMWare are liable.